This invention relates to an aerobic sewage treatment system, primarily intended for smaller capacity use, in which the outlet sewage line empties into a tank, and the sewage collected therein is treated and decomposed by the aerobic process. The process itself is well known, and systems of this type presently exist for handling large volumes of sewage, for example municipal or factory sewage treatment systems, and to a lesser degree aerobic systems are utilized for residences, where the sewage for one or a small number of residences is so treated.
Typical of the larger municipal or commercial type systems are those shown in U.S. Pat. Nos. 3,827,679, 3,865,721, and 2,082,759 wherein a large motor driven pump or impeller is mounted to circulate the sewage deposited within a tank. The impeller may be supported on a shaft within a venturi or the like, and an air injection line is directed into or near the throat of the venturi, where a lower pressure exists as the result of the induced flow there through, causing the air or oxygen to be drawn into and mixed with the flow as it passes through the venturi.
Smaller aerobic systems, intended primarily for residential use, are typified by the arrangments shown in U.S. Pat. Nos. 2,987,186, and 3,149,071, where a motor is mounted in a housing near the top of the tank and drives an air injecting impeller device through a long shaft. Usually this shaft is hollow and air is drawn into the top of the shaft and passes through a plurality of outlets from the impeller which is positioned within the pool of sewage in the tank. Rotation of the impeller, which may be no more than radially extending tubes, causing a turbulent mixing action of the sewage and also inducing a flow of air through the hollow shaft and the outlets into the disturbed pool of sewage surrounding the impeller device.